A series of new studies based on Curiosity data shows that the rover's landing area was once the site of a potentially life-friendly lake.

The Curiosity rover's harrowing landing in Gale Crater riveted the world last August. Now sediments found by Curiosity indicate that the rover's landing site once hosted lakes that could have supported life. The findings were announced in a paper published today by the journal Science, one of several new studies based on Curiosity's data.

John Grotzinger, a geologist at Caltech and Curiosity science chief, led a team that found the evidence for an ancient lake in a 5-foot-thick layer of rock found in an area of Gale Crater named Yellowknife Bay. The layer of rock, called the Sheepbed mudstone, has several qualities that indicate it formed in an environment that was hospitable to life. First, the thickness of the rock indicates that the lake existed in that area for a long period of time. Second, chemical analysis showed that the lake had all the right ingredients for life. According to Grotzinger, the lake would have been roughly half the size of one of the Finger Lakes in upstate New York.

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The mudstone formed in an environment similar to the one at the bottom of any lake here on Earth. "It's literally the mud that would squish between your toes," Grotzinger says.

It takes a long time for sediments to be deposited at the bottom of a lake. Fine particles of rock, carried along in the rush of a river or stream, lose their momentum when a river empties into a still lake, and slowly drift to the bottom. On average, 3 feet of sediment accumulate over 1000 years. But this rate can be faster or slower, depending on the surrounding environment, and the Sheepbed mudstone likely formed over the course of perhaps tens of thousands of years. Scientists estimate in the paper that the lake was probably part of an even larger system of rivers, lakes, and groundwater, creating an environment that would have been capable of supporting life for millions (even tens of millions) of years.

The chemical composition of the rock would have been the perfect habitat for a kind of bacteria called chemolithoautotrophs. "These are simple microorganisms that feed on chemicals from rocks," Grotzinger says. Analysis of the rocks showed that they contained minerals with carbon, hydrogen, oxygen, nitrogen, sulfur, and phosphorus, the six elements most common to life on Earth. Curiosity also found minerals such as magnetite, and sulfate and sulfide minerals, which ancient microbes would have been able to use as a potential source of energy.

The presence of clay-rich minerals in the rock indicates that the water in the lake was relatively fresh water, making it potentially habitable to a broader range of microbes than it would have been has it been highly acidic or highly saline. "It's the kind of water where if you were really dying, you could drink it, but you probably wouldn't bottle it for resale." Grotzinger says.

Science/AAAS

Texture of the "snake" as seen by MAHLI on Sol 149 (6 January, 2013). Note the uniformly fine grain size and presence of pits that may reflect void spaces and, in some cases, erosion of softer components that may represent intraclasts. Science/AAAS

But just because the lake had the potential to support life doesn't mean that it did. And just to make things even more difficult: Even if there were evidence for life here, it would be nearly impossible to distinguish that evidence from the naturally occurring geological formations that surround it. "We have no way on this mission to tell the difference between something that is biologic origin or abiologic origin," Grotzinger says.

Even if there were fossils in the mudstone, Curiosity doesn't have the right kind of equipment to see them. That job will be left to the Mars rover set to launch in 2020, which might have the capability to collect rocks on Mars and bring them back to Earth for more detailed analysis.